Method for surface treating a substrate

ABSTRACT

A method for surface treating a substrate includes following steps. Firstly, a substrate including a metallic surface capable of being electroplated with a metal coating is provided. Secondly, a first metal coating is electroplated onto the metallic surface of the substrate. Thirdly, an oxidized metal film is formed to cover the first metal coating. The first metal coating of substrate is blasted using quartz sand. The oxidized metal film is removed from the first metal coating. The second metal coating is electroplated onto the first metal coating.

BACKGROUND

1. Field of the Invention

The present invention relates to a method for surface treating a substrate.

2. Discussion of the Related Art

Mobile devices, such as mobile telephones, personal digital assistants, or MP3 players, enable consumers to enjoy the convenience of high technology services, almost anytime and at virtually any location. These mobile devices often employ a variety of decorative housings to attract consumers. Electroplating is an attractive and effective process for improving corrosion resistance and metallic appearance of the housings. Many housings for mobile devices are processed to form metal coatings on surfaces thereof by electroplating.

However, electroplated housings can be excessively bright and cause discomfort to the users.

Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the method for surface treating a substrate can be better understood with reference to the following drawing. The components in the drawing are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the method for surface treating a substrate.

The FIGURE is a flow chart of an exemplary embodiment of a method for surface treating a substrate.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to the FIGURE, a method for surface treating a substrate may include the steps S100 to S600.

In step S100, a substrate is provided. The substrate includes a metallic surface capable of being electroplated with a metal coating.

According to the exemplary embodiment, the substrate is made of plastic selected from a group consisting of acrylonitrile butadiene styrene (ABS), poly methyl methacrylate (PMMA), and polycarbonate (PC). The substrate is metalized by wet chemical deposition. During wet chemical deposition, a surface of the substrate to be metalized is firstly etched so that the surface is roughened. The etching of the substrate allows an activating layer in a subsequent process to be attached to the roughened surface. The etching process may be carried out, for example, in chromic acid, chromosulfuric acid, or potassium permanganate etching solution. An associated cleaning step is then carried out for cleaning the substrate. Subsequently, the surface of the substrate is activated in such manner that active metal particles, i.e., noble metal particles, are deposited on the surface of the substrate when being immersed into an activating solution containing hydrochloric acid, polyamide acid, and noble metal salt. During activation, the noble metal particles are separated out from the activating solution, dispersed, and deposited on the surface of the substrate. The noble metal salt may include palladium salt. After being activated, the substrate is rinsed with water and then metalized with chemical plating in a copper electrolyte containing copper salt and sulfuric acid, thereby depositing a chemical copper coating on the substrate. As such, the surface of the substrate is metalized. It should be understood that the substrate can instead be made of metal selected from a group consisting of steel, aluminum, titanium, magnesium, and alloys thereof.

In step S200, a first electroplated metal coating is deposited onto the metalized surface of the plastic substrate by electroplating. The first electroplated metal coating may include copper. The electroplating may be carried out by immersing the substrate into an electrolyte including at least one of copper sulfate and copper pyrophosphate, with the metalized surface of the plastic substrate being a cathode, and a copper anode being provided and immersed in the electrolyte. The thickness of the first electroplated metal coating is in a range from about 10 to about 50 microns.

In step S300, the first electroplated metal coating is passivated (i.e., has its chemical reactivity reduced) in an oxidizing agent containing chromic acid or chromate salt. That is, the first electroplated metal coating is oxidized to form an oxidized metal film coated thereon, which may protect the first electroplated metal coating from moisture corrosion.

In step S400, the passiviated first electroplated metal coating then undergoes sand blasting. During the sand blasting process, a mixture of quartz sand and water in an air sand blower strike the passiviated first electroplated metal coating, to put a plurality of dispersed and distributed dents in the passiviated first electroplated metal coating. The dents cause the first electroplated metal coating to possess a dull frosted appearance, which may be more attractive to consumers. The oxidized metal film is partially struck away from the first electroplated metal coating by sand blasting, thereby partially exposing the first electroplated metal coating.

In step S500, the first electroplated metal coating is repeatedly passivated in the oxidizing agent so as to passiviate the exposed portion thereof.

In step S600, the first electroplated metal coating is activated to remove the oxidized metal film that covers the first electroplated metal coating. The activation is carried out in an electrolyte including sodium hydroxide by an electric current.

In step S700, the substrate is immersed into hydrofluoric acid to remove the residual quartz sand on the first electroplated metal coating.

In step S800, a second electroplated metal coating is electroplated onto the first electroplated metal coating. The second electroplated metal coating may be made one of palladium and alloys of tin and copper. The thickness of the second electroplated metal coating is in a range from about 2 to about 8 microns and less than that of the first electroplated metal coating. It should be understood that, the second electroplated metal coating can be further coated with a decorative coating made of chrome, which has a thickness in a range from about 0.1 to about 2 microns and less than that of the second electroplated metal coating. The first electroplated metal coating and the second electroplated metal coating may give the substrate a dull frosted appearance attractive to consumers.

It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention. 

1. A method for surface treating a substrate, comprising the steps of: providing a substrate including a metallic surface capable of being electroplated with a metal coating; electroplating a first metal coating onto the metallic surface of the substrate; passivating the first metal coating by immersing the substrate into an oxidizing agent to forming an oxidized metal film covering the first metal coating; sand blasting the first metal coating of substrate; activating the first metal coating by removing the oxidized metal film from the first metal coating; and electroplating a second metal coating onto the first metal coating.
 2. The method as claimed in claim 1, wherein the substrate is made of plastic, the substrate being metalized by wet chemical deposition.
 3. The method as claimed in claim 2, wherein the metallization of the substrate comprises steps of forming a noble metal coating on the substrate and plating a copper layer onto the noble metal coating in a copper electrolyte containing copper salt and sulfuric acid.
 4. The method as claimed in claim 2, wherein the substrate is made of plastic selected from a group consisting of acrylonitrile butadiene styrene, poly methyl methacrylate, and polycarbonate.
 5. The method as claimed in claim 1, wherein the substrate is made of metal selected from a group consisting of steel, aluminum, titanium, magnesium, and alloys thereof.
 6. The method as claimed in claim 1, wherein the first metal coating is made of copper.
 7. The method as claimed in claim 1, wherein the thickness of the first metal coating is in a range from about 10 to about 50 microns.
 8. The method as claimed in claim 1, wherein the oxidizing agent includes one of chromic acid and chromate salt.
 9. The method as claimed in claim 1, wherein the step of sand blasting the first metal coating is carried out using a mixture of quartz sand and water in an air sand blower to strike the first metal coating, to put a plurality of dispersed and distributed dents in the first metal coating.
 10. The method as claimed in claim 1, further comprising a step of repeatedly passivating the first metal coating by immersing the substrate into the oxidizing agent after the sand blasting.
 11. The method as claimed in claim 9, further comprising a step of immersing the substrate into hydrofluoric acid to remove residual quartz sand particles from the first metal coating.
 12. The method as claimed in claim 1, wherein the second metal coating is made of copper and has a thickness less than that of the first metal coating.
 13. The method as claimed in claim 1, wherein the thickness of the second metal coating is in a range from about 2 to about 8 microns.
 14. The method as claimed in claim 1, wherein the second metal coating is coated with a decorative coating made of chrome, which has a thickness less than that of the second metal coating.
 15. The method as claimed in claim 14, wherein the decorative coating is in a range from about 0.1 to about 2 microns.
 16. A method for surface treating a substrate, comprising the steps of: providing a substrate including a metallic surface capable of being electroplated with a metal coating; electroplating a first metal coating onto the metallic surface of the substrate; forming an oxidized metal film covering the first metal coating; sand blasting the first metal coating of substrate; removing the oxidized metal film from the first metal coating; and electroplating a second metal coating onto the first metal coating.
 17. The method as claimed in claim 16, wherein the first metal coating is made of copper and has a thickness in a range from about 10 to about 50 microns.
 18. The method as claimed in claim 16, wherein the second metal coating is made of copper and has a thickness less than that of the first metal coating.
 19. The method as claimed in claim 18, wherein the thickness of the second metal coating is in a range from about 2 to about 8 microns.
 20. The method as claimed in claim 16, wherein the second metal coating is coated with a decorative coating made of chrome, which has a thickness in a range from about 0.1 to about 2 microns less than that of the second metal coating. 